1. Field of the Invention
The present invention relates to network interfacing, and more particularly to methods and systems for controlling transmission of data between network stations connected to a telephone line medium.
2. Background Art
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface cards at each station to share access to the media.
Conventional local area network architectures use a media access controller operating according to half-duplex or full duplex Ethernet (ANSI/IEEE standard 802.3) protocol using a prescribed network medium, such as 10BaseT. Newer operating systems require that a network station be able to detect the presence of the network. In an Ethernet 10BaseT environment, the network is detected by the transmission of a link pulse by the physical layer (PHY) transceiver. The periodic link pulse on the 10BaseT media is detected by a PHY receiver, which determines the presence of another network station transmitting on the network medium based on detection of the periodic link pulses. Hence, a PHY transceiver at station A is able to detect the presence of station B, without the transmission or reception of data packets, by the reception of link pulses on the 10BaseT medium from the PHY transmitter at station B.
Efforts are underway to develop an architecture that enables computers to be linked together using conventional twisted pair telephone lines instead of established local area network media such as 10BaseT. Such an arrangement, referred to herein as a home network environment, provides the advantage that existing telephone wiring in a home may be used to implement a home network environment. However, telephone lines are inherently noisy due to spurious noise caused by electrical devices in the home, for example dimmer switches, transformers of home appliances, etc. In addition, the twisted pair telephone lines suffer from turn-on transients due to on-hook and off-hook and noise pulses from the standard POTS telephones, and electrical systems such as heating and air-conditioning systems, etc.
An additional problem in telephone wiring networks is that the signal condition (i.e., shape) of a transmitted waveform depends largely on the wiring topology. Numerous branch connections in the twisted pair telephone line medium, as well as the different associated lengths of the branch connections, may cause multiple signal reflections on a transmitted network signal. Telephone wiring topology may cause the network signal from one network station to have a peak to peak voltage on the order of 10 to 20 millivolts, whereas network signals from another network station may have a value on the order of one to two volts. Hence, the amplitude and shape of a received pulse may be so distorted that recovery of a transmitted clock or transmit data from the received pulse becomes substantially difficult.
An additional problem encountered in European telephone systems involves the use of a network termination basic access (NTBA) device, used as an interface between the residential customer premises and a central office of the public switched telephone network for transmission of Integrated Services Digital Network (ISDN)-based signals. In particular, NTBA devices map a two wire ISDN signal from a central office into a four wire S0 bus having a two wire send path and a two wire receive path for sending and receiving the ISDN-based signals throughout a customer premises. The ISDN-based signals generate harmonic reflections on the S0 bus that cause substantial interference with the higher-frequency network signals. Moreover, the zero crossing of an ISDN-based signal interferes substantially with the transmitted network signals, rendering the transmitted network signal unusable due to the harsh conditions on the four wire S0 signal bus.
In addition, manufacturers of NTBA devices and ISDN terminal devices may have internal capacitors to minimize electromagnetic interference (EMI) of the devices. These internal capacitors, however, induce capacitive loads on the bus. These capacitive, while compliant with ISDN amplitude and timing requirements, severely attenuate the higher frequency network signals and substantially limit the distance that the network signals can be transmitted.
There is need for an arrangement for interconnecting computer end stations in a home telephone network having a network termination basic access (NTBA) device and configured for sending ISDN-based signals on a four-wire bus.
There is also a need for an arrangement for a universal coupling mechanism for home networking signals on a four-wire S0 bus, regardless of variations in S0 bus circuitry within ISDN end equipment such as network terminators, private branch exchange (PBX) systems, or internal S0 bus systems of modem PBX systems.
These and other needs are attained by the present invention, where filters are coupled between each ISDN device and the four-wire S0 bus, insuring that the four-wire S0 bus is isolated from the capacitive influences of the ISDN devices. This isolation of the S0 bus insures the proper transmission of the higher frequency home network signals.
One aspect of the present invention provides a method of implementing a local area network in a home telephone network having a connector, configured for sending and receiving ISDN-based signals to and from a public switched telephone network, and a four-wire bus. The four-wire bus includes a two-wire send path and a two-wire receive path for sending and receiving the ISDN-based signals, respectively, between the connector and connected ISDN terminal devices. The method includes connecting a low pass filter between the two wires of the two-wire send path at an output terminal of the connector, the low pass filter configured for passing the ISDN-based signals and rejecting harmonics thereof and isolating capacitive influences of the connector from the two-wire send path. The method also includes isolating capacitive influences of each of the connected ISDN terminal devices from the two-wire send path, and transmitting by a network node a first home network signal onto the two-wire send path and a second home network signal, complementary to the first home network signal, onto the two-wire receive path. Connection of the low pass filter insures that any harmonics of the ISDN-based signals to not interfere with the home network signals. Moreover, the isolation of each of the connected ISDN terminal devices insures that the circuitry within the ISDN terminal devices does not induce any capacitive loads onto the two-wire send path that may adversely affect transmission of the home network signals. Finally, the transmission of the first and second home network signals onto the two-wire send path and the two-wire receive path enables the two-wire home network signal to be transmitted onto a four-wire bus, substantially increasing the effective diameter of the transmission medium and greatly improving transmission performance.
Another aspect of the present invention provides a computer network. The computer network includes a connector configured for sending and receiving ISDN-based signals to and from a public switched telephone network. The computer network also includes a four-wire bus having a two-wire send path and a two-wire receive path for sending and receiving the ISDN-based signals between the connector and ISDN terminal devices. A low pass filter, coupled between the two-wire send path and the connector, is configured for isolating capacitive influences of the connector from the two-wire send path and filtering ISDN harmonic signals occurring substantially at the frequencies of network data signals. The computer network also includes ISDN terminal filters, each configured for isolating capacitive influences of a corresponding one of the ISDN terminal devices from the two-wire send path, and first and second end stations configured for exchanging the network data signals at frequencies substantially higher than the ISDN-based signals via at least one of the two-wire send path and the two-wire receive path.
Additional advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of instrumentalities and combinations particularly pointed in the appended claims.